I've been making progress with fighting my impostor syndrome.

Some things I learned, maybe they're helpful for other people as well:
Impostor Syndrome is not your fault. It is most likely an effect of the environment you grew up in, which told you that you couldn't do things, that your opinions didn't matter, that you were not enough.
This kind of social conditioning has drastic effects and is hard to fight. You can't "get over it" just like that. Don't beat yourself up for that.

Something that helped me fight impostor syndrome:

Having my contributions acknowledged and appreciated by my peers.
If your peers never give you that, consider finding other peers.

I know it's not easy to find other peers, whether at a tech job or in a non-work tech context. Toxic people are everywhere and some of them them are very loud. Others are quieter, but still hold you back, make you feel like you're less than them.
Try to find good boundaries with them. Only engage with them when you must. Find others who don't make you feel shitty, but support you.

Find senior people in your field and in your tech communities who are friendly, who will give you feedback that is useful to you, who will give you advice, who will introduce you to the right people.
They exist, in my experience.

Use any mentoring program that exists. If you're wondering if you're "enough" to use this resource, you definitely are. These programs exist exactly for you, if they are any good.
However, they are often very career-focused and not very emotional. Try to find someone to talk about the emotional side, too.

If you're working with a senior, such as an advisor, reflect on how working with them makes you feel, how much they overtly value and endorse your work, how much credit they take for it and how much of the credit they give to you.
Asking for being given credit and for being given space is terrifying. Don't beat yourself up if you can't. Take the experience as a data point of what kind of person not to work with.

Another thing that helps me fight impostor syndrome:

Talk about your work positively. If you implement something, that's awesome! Sure, there are challenges, but designing and implementing systems is hard. You're making experiences that can be very very valuable for others working on the same problem.

If you don't understand something when trying to implement something, especially a standard, that's probably not because you are stupid, which you are not.
That's probably because it could have been explained better. Asking for clarification can be a great contribution. Others probably had the same question, but were afraid to ask questions. Maybe everyone understands this thing differently. Having such a thing pointed out is extremely valuable.